In normal voice recognition, a speech uttered from a mouth is recorded through a close-talking type microphone, and is subjected to a recognition process. On the other hand, there are lots of applications, such as interaction with a robot, operation of an in-vehicle device like a car navigation system through a speech, and creation of conference minutes, where enforcing a user to use a close-talking type microphone is unnatural. In such applications, it is desirable that a speech should be recorded through a microphone provided at a system side and should be subjected to a recognition process. In a case where speech recording and voice recognition are performed through a microphone provided away from an utterer, however, an S/N ratio is deteriorated, it is difficult to hear, and the accuracy of voice recognition is extremely reduced.
In response to such problems, there is an attempt that a desired speech is selectively recorded by controlling the directivity using a microphone array. As such devices which control the directivity using a few microphones, there are an ultra directional microphone using two single-directional microphone units (see, patent literature 1) and a recording device for multi-channel stereo using four non-directional microphones (see, patent literature 2). Further, there is a microphone device having three pairs of microphones disposed around a base microphone (see, patent literature 3).
Moreover, there is proposed a scheme called SAFIA which separates a sound by utilizing a difference between sound pressures, reaching individual microphones and caused due to differences in positional relationships between the individual microphones and a sound source (see, patent literature 4). The scheme called SAFIA is a sound separation technique which causes output signals of a plurality of fixed microphones to undergo narrow-band spectrum analysis, and for a microphone that gives the largest power for each frequency band, performs band selection of assigning a sound of that frequency band to that microphone (see FIG. 8 to be discussed later).    Patent Literature 1: Japanese Unexamined Patent Publication No. H10-126876 (claim 1, FIGS. 1 and 2, and abstract)    Patent Literature 2: Japanese Unexamined Patent Publication No. 2002-223493 (claim 1, FIGS. 1 and 3, and abstract)    Patent Literature 3: Japanese Unexamined Patent Publication No. 2002-271885 (claim 1, FIGS. 1 and 11, and abstract)    Patent Literature 4: Japanese Patent Publication No. 3355598 (paragraphs 0006, 0007, FIG. 1 and abstract)